Open Stack

[This is Horizon-related but affects every service in OpenStack, hence no
filter in the subject]

I would like for OpenStack to support browser-based Javascript API clients.
Currently this is not possible because of cross-origin resource blocking in
Javascript clients - that is, given some Javascript hosted on
"https://horizon.company.com/" you cannot, for example, call from that
Javascript code to an API on "https://apis.company.com:5000/v2.0/tokens" to
authenticate with Keystone.

There are three solutions to this problem:

1. the Horizon solution, in which those APIs are proxied by a very thick
   layer of additional Python API, plus some Python view code with some
   Javascript on the top only calling the Horizon view code,
2. add CORS support to all the OpenStack APIs though a new WSGI middleware
   (for example oslo.middleware.cors) and configured into each of the API
   services individually since they all exist on different "origin"
   host:port combinations, or
3. a new web service that proxies all the APIs and serves the static
   Javascript (etc) content from the one origin (host). APIs are then served
   from new URL roots "/name/" where the name is from the serviceCatalog
   entry. Static content can be served from "/static/". The serviceCatalog
from
   keystone will be rewritten on the fly to point the API publicURLs at the
   new service. Requests are no longer cross-origin.

I have implemented options 2 and 3 as an exercise to see how horrid each one
is.


== CORS Middleware ==

For those wanting a bit of background, I have written up a spec for oslo
that
talks about how this could work: https://review.openstack.org/#/c/119485/

The middleware option results in a reasonably nice bit of middleware. It's
short and relatively easy to test. The big problem with it comes in
configuring it in all the APIs. The configuration for the middleware takes
two forms:

1. hooking oslo.middleware.cors into the WSGI pipeline (there's more than
   one in each API),
2. adding the CORS configuration itself for the middleware in the API's main
   configuration file (eg. keystone.conf or nova.conf).

So for each service, that's two configuration files *and* the kicker is that
the paste configuration file is non-trivially different in almost every
case.

That's a lot of work, and confusing for deployers. Configuration management
tools can ease *some* of this burden (the *.conf files) but those paste
files
are a bit of a mess :(

Once the config change is in place, it works (well, except for an issue I
ran
into relating to oslo.middleware.sizelimit which I'll go into in another
place).

The implementation hasn't been pushed up for review as I'm not sure it
should
be. I can do this if people wish me to.


== New Single-Point API Service ==

Actually, this is not horrid in any way - unless that publicURL rewriting
gives you the heebie-jeebies.

It works, and offers us some nice additional features like being able to
host
the service behind SSL without needing to get a bazillion certificates. And
maybe load balancing. And maybe API access filtering.

I note that https://openrepose.org already exists to be *something* like
this, but it's not *precisely* what I'm proposing. Also Java euwww ;)


So, I propose that the idea of CORS-in-all-the-things as an idea be
put aside as unworkable.

I intend to pursue the single-point API service that I have described as a
way of moving forward in prototyping a pure-Javascript OpenStack Dashboard.
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